This invention relates to a semiconductor tester with power assist for vertical test head movement.
A known type of semiconductor tester includes a test head having an array of terminals exposed at an interface surface of the test head for engaging corresponding terminals of a load board on which a semiconductor device under test (DUT) is mounted in order to effect electrical connection between the terminals of the test head and corresponding pins of the DUT.
The tester is used in conjunction with an interfacing mechanism, such as a wafer prober or an integrated circuit device handler, for delivering semiconductor devices in succession to a test location at which an individual DUT is mounted to the load board and a test is performed. There are numerous makes and models of such interfacing mechanisms and different interfacing mechanisms have different requirements for the orientation of the DUT in the test location. A given tester should be useable with a variety of these interfacing mechanisms and it may be necessary from time to time to change the location and/or orientation of the test head. For this purpose, the test head is attached to a support frame by a manipulator which guides movement of the test head along a vertical axis and two mutually perpendicular horizontal axes, and may also permit rotational movement of the test head.
When the tester is to be used with a different interfacing mechanism, the operator must carefully position the test head at the proper location and in the proper orientation to engage the load board. It is necessary to avoid collision when the test head is moved or re-oriented since this may cause damage to the test head or other equipment.
The moving mass of the test head and manipulator mechanism may be quite substantial. It is known to use a counterbalance mechanism to support the weight of a massive object that is to be moved vertically, but even if the weight of the counterbalance is equal to the weight of the object to be moved, substantial forces may still be necessary to bring about movement of the object since it is necessary to overcome the inertia of rest and frictional resistance.
It is conventional to use a power operated mechanism to move a massive object. For example, in a gantry crane, electric or hydraulic motors are used to drive a lifting device along two mutually perpendicular horizontal axes. Such power operated mechanisms generally include a three position switch (e.g. forward, stop, reverse) for each axis, and the operator positions the switch at forward for movement in one direction along a selected axis, reverse for movement in the other direction along the selected axis, and stop for no movement along that axis. This type of mechanism is subject to disadvantage because the operator must control the switches by observation of the position of the lifting device, and if the operator misjudges the position of the lifting device, there is a danger of collision. Further, these mechanisms do not allow the operator to adjust the speed of movement of the lifting device along a selected axis.